Vanadium removal from roasted LD converter slag: Optimization of parameters by response surface methodology (RSM)

Alkaline roasting-sulfuric acid leaching process was used to remove vanadium from LD (Linz Donawitz) converter slag. Leaching parameters were investigated and optimized in order to maximize the recovery of vanadium as the vanadium content in the slag is low. The independent leaching factors investigated were liquid to solid ratio (L/S) (10-20 mL/g), temperature (40-70 °C), sulfuric acid concentration (1.5-3.0 M), stirring rate (500-700 rpm) and time (60-120 min). Response surface methodology (RSM) was used to optimize the process parameters. To choose the best model for describing the leaching process, Box-Cox power transformation technique was used which in turn was used to normalize the data. The most influencing parameter was found to be L/S and the less effective was stirring rate as well. Based on the results, optimum removal condition (approx. 96%) according to process parameters was obtained with L/S ratio of (19.99), temperature of (70 °C), sulfuric acid concentration of 2.05 M, rpm of (558) and leaching time of (60 min), respectively.